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1.
Marta Bugaj Piotr A. Baran Piotr Bernatowicz Patrycja Brożek Krystyna Kamieńska‐Trela Adam Krówczyński Bohdan Kamieński 《Magnetic resonance in chemistry : MRC》2009,47(10):830-842
A series of aryl‐substituted enaminoketones and their thio analogues in CDCl3 solution and in the solid state were studied by the use of high‐resolution 1H and 13C as well as 13C cross polarization magic angle spinning (CP MAS) NMR spectra in combination with gauge including atomic orbitals‐density functional theory (GIAO‐DFT) calculations performed at the B3PW91/6–311 + + G(d,p) level of theory using the B3PW91/6‐311 + + G(d,p)‐optimized geometries. The analysis of the 13C NMR spectra in solution was done by using the Incredible Natural Abundance DoublE QUAntum Transfer Experiment (INADEQUATE) technique, whereas trends observed in the 13C shielding constants, calculated for the compounds studied, were a great help in assigning most of the signals in the 13C CP MAS NMR spectra. It was established on the basis of the experimental and theoretical NMR data that both groups of compounds exist in the form of Z‐s‐Z‐s‐E isomers in CDCl3 solution as well as in the solid state, with the NH hydrogen atom involved in intramolecular hydrogen bonding. This conclusion is in agreement with the fact that some of the compounds studied reveal liquid‐crystalline properties. Three‐bond H, H and C, H coupling constants measured in solution played a crucial role in the structure elucidation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
2.
(1)H and (13)C NMR data for N-substituted morpholines 1-20 were measured using 1D (DEPT, 1D NOE difference) and 2D NMR spectroscopic methods including (1)H-(1)H COSY, long-range (1)H-(1)H COSY, NOESY, gHMBC and gHMQC experiments. At room temperature the (1)H NMR spectra of protonated compounds 2 and 9 show the chair conformation for the morpholine ring. Spin-spin coupling constants were deduced from the resolution-enhanced proton spectra. 相似文献
3.
Hung I Macdonald CL Schurko RW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(23):5923-5935
The correlation between anisotropic 9Be NMR (quadrupolar and chemical shielding) interactions and the structure and dynamics in [Cp2Be], [Cp2*Be], and [(C5Me4H)2Be] is examined by solid-state 9Be NMR spectroscopy, as well as by ab initio and hybrid density functional theory calculations. The 9Be quadrupole coupling constants in the three compounds correspond well to the relative degrees of spherical ground-state electronic symmetry of the environment about beryllium. Theoretical computations of NMR interaction tensors are in excellent agreement with experimental values and aid in understanding the origins of NMR interaction tensors and their correlation to molecular symmetry. Variable-temperature (VT) 9Be and 13C NMR experiments reveal a highly fluxional structure in the condensed phase of [Cp2Be]. In particular, the pathway by which the Cp rings of [Cp2Be] 'invert' coordination modes is examined in detail using hybrid density functional theory in order to inspect variations of the 9Be NMR interaction tensors. The activation energy for the 'inversion' process is found to be 36.9 kJ mol(-1) from chemical exchange analysis of 13C VT CP/MAS NMR spectra. The low-temperature (ca. -100 degrees C) X-ray crystal structures of all three compounds have been collected and refined, and are in agreement with previously reported structures. In addition, the structure of the same Cp2Be crystal was determined at 20 degrees C and displays features consistent with increased intramolecular motion, supporting observations by 9Be VT NMR spectroscopy. 相似文献
4.
We have performed the direct measurements of 13C magnetic shielding for pure liquid TMS, solution of 1% TMS in CDCl3 and solid fullerene. The measurements were carried out in spherical ampoules exploring the relation between the resonance frequencies, shielding constants and magnetic moments of 13C and 3He nuclei. Next the 13C shielding constants of glycine, hexamethylbenzene and adamantane were established on the basis of appropriate chemical shifts measured in the solid state. All the new results are free from susceptibility effects and can be recommended as the reference standards of 13C shielding scale in the magic angle spinning NMR experiments. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
5.
Data from two-dimensional (2D) NMR experiments were used to identify the reaction products resulting from the opening of pyroglutamates with isocyanates or thioisocyanates. The reaction has the potential to produce compounds that would have very similar one-dimensional proton ((1)H) or carbon-13 ((13)C) NMR spectra. Careful analysis of (1)H--(1)H COSY, (1)H--(1)H NOESY, and HMBC data, including chemical shifts and coupling constants, were used to distinguish correctly between carbamoyl-2-pyrrolidinone, hydantoin, and perhydro-1,3-diazepine-2,4-dione type structures that could result from this reaction. This work describes their preparation and subsequent identification using 2D NMR spectroscopy, and includes complete (13)C assignments of the reaction products. The 2D NMR techniques and analysis described here can be applied successfully to other synthetic reactions with the potential to produce isomeric products. 相似文献
6.
Fuente A Reyes M Alvarez YM Ruiz JA Vélez H Viñas-Bravo O Montiel-Smith S Meza-Reyes S Sandoval-Ramírez J 《Magnetic resonance in chemistry : MRC》2005,43(8):676-678
(1)H and (13)C NMR spectroscopic data for 5alpha-androstanes and halo-5alpha-androstanes with different substituents at positions C-3, C-9, C-11 and C-17 were examined and assigned by a combination of 1D and 2D NMR experiments. The substituent effects on the (13)C chemical shifts were compared with those of epi-androsterone, used as a reference compound. The coupling constants (n)J((19)F,(13)C) were measured for compounds 6, 8, 11 and 14. 相似文献
7.
13C cross-polarization magic angle spinning (CP/MAS) NMR data for 2,2,5,7,8-pentamethylchroman-6-ol (2), 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox c) (3) and its acetate (4), 2-methoxy-2,2,5,7,8-pentamethylchroman-6-ol (5), 2-hydroxy-2,2,5,7,8-pentamethylchroman-6-ol (6) and 2,2,5,7,8-pentamethylchroman (7) are reported. A deshielding of 7.7 ppm for the carboxylic carbon was observed in solid Trolox due to formation of intermolecular hydrogen bonds within cyclic dimers. Such crystal packing permits effective cross-polarization and fast relaxation (short T1rho(H)). The impact of the proton concentration on the CP dynamics is reflected by the longer T(CP) and T1rhoH for Trolox-d2 (deuterated at mobile proton sites). The calculated GIAO RHF shielding constants are sensitive to intramolecular effects: rotation around the C-6-O bond (changes of sigma up to 8 ppm) and conformation at C-2. 相似文献
8.
《Magnetic resonance in chemistry : MRC》2002,40(5):353-360
The 15N NMR chemical shifts of N7‐ and N9‐substituted purine derivatives were investigated systematically at the natural abundance level of the 15N isotope. The NMR chemical shifts were determined and assigned using GSQMBC, GHMBC, GHMQC and GHSQC experiments in solution. 15N cross‐polarization magic angle spinning data were recorded for selected compounds in order to study the principal values of the 15N chemical shifts. Geometric parameters obtained by using RHF/6–31G** and single‐crystal x‐ray structural analysis were used to calculate the chemical‐shielding constants (GIAO and IGLO) which were then used to assign the nitrogen resonances observed in the solid‐state NMR spectra and to determine the orientation of the principal components of the shift tensors. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
9.
10.
(27)Al, (17)O and (13)C chemical shieldings of aluminum acetylacetonate complex, Al(acac)(3), were calculated at some Density Functional Theory (DFT) levels of theory. In these calculations the X-ray structures of its different polymorphs were used. Using these calculated data observed discrepancies between the X-ray crystallography and solid state NMR experiment were explained in terms of the quality of the NMR data. In this survey we resorted to the simulated spectra using our calculated chemical shifts. In order to confirm our conclusions, electric field gradient (EFG) tensors of the (27)Al and (17)O nuclei were calculated at the same levels of theory as used in the chemical shielding calculations. On the other hand, these calculated chemical shifts and nuclear quadrupole coupling constants (NQCCs) made a correlation between X-ray crystallography and solid state NMR experiments. 相似文献
11.
《Magnetic resonance in chemistry : MRC》2002,40(3):219-224
An extensive study of both liquid‐ and solid‐state NMR spectroscopy was undertaken in order to elucidate the structural features of a phenyleneterephthalamide oligomer (OPTA) and of some related diarylamides. 1D‐ and 2D‐COSY measurements allowed us to assign completely the proton signals of the title compounds in solution, while 1D‐, 2D‐HETCOR and 2D‐COLOC measurements were used to assign 13C resonances. Solid‐state 13C NMR experiments, by conventional cross‐polarization (CP) at different contact times and with the dipolar dephased CP technique, were used to characterize these molecules in the solid state. Such techniques allowed us to differentiate among different carbon atoms; in the resulting spectra it was then possible to observe the selective appearance of signals from protonated and quaternary carbon atoms. It was also ascertained that the limited structural mobility of the insoluble OPTA, existing as a single monophasic species, can be explained in terms of hydrogen‐type bonds present in the solid state. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
12.
HOU Guangjin WANG Liying LU Xiaoming ZHENG Anmin DENG Feng &YE Chaohui . Department of Physics Huazhong University of Science Technology Wuhan China . State Key Laboratory of Magnetic Resonance Atomic Molecular Physics Wuhan Institute of Physics Mathematics Chi-nese Academy of Sciences Wuhan China . Department of Chemistry Capital Normal University Beijing China 《中国科学B辑(英文版)》2004,47(3)
~~Experimental and theoretical study of~(13)C shielding tensors in new-style molybdenum complex~~ 相似文献
13.
Katritzky AR Akhmedov NG Wang M Rostek CJ Steel PJ 《Magnetic resonance in chemistry : MRC》2004,42(12):999-1011
Regioselective addition of allylthiol at the C-3 position adjacent to the nitrogen carrying the phenyl group of the 1,4-phenylenediamine moiety of compounds 1-4 was rigorously confirmed by 1D NOE difference in combination with gHMBC experiments. The structures of 1,4-phenylenediamines 1-4, allylsulfanyl-N1-alkyl-N4-phenyl-1,4-phenylenediamines 5-8 and cyclization products 9-14 were completely analyzed in both CDCl3 and DMSO-d6 solutions. The 1H and 13C NMR spectra of 10 and 11, which contain two chiral centers, exhibit duplication for several signals, indicating the existence of two diastereomeric forms. The full structures of 5 and 9 were unambiguously confirmed by x-ray crystallography. The 1H and 13C NMR spectra of all compounds were assigned using one- and two-dimensional NMR techniques (APT, DEPT, 1D NOE difference, COSY, NOESY, HETCOR, gHMQC and gHMBC). 相似文献
14.
The stereochemistry of gamma-butyrolactons tetrahydro-6a-phenylfuro[3,4-b]furan-2(3H)-one (1), 1,4,5,9b-tetrahydro-3a-methylnaphtho[2,1-b]furan-2(3aH)-one (2), 1,4,5,9 b-tetrahydro-3a-methylfuro[2,3-c]quinolin-2(3aH)-one (3) and hexahydro-furo[3,2-c]benzofuran-2-one (4) was studied using DPFGSE-NOE experiments. Compounds 1-3 contain two stereocenters, while 4 contains three. Both (1)H and (13)C spectra showed a single diastereomer of all the compounds. Routine 2D experiments (DQF)-COSY, HMQC/HSQC, and HMBC were used to assign (1)H and (13)C spectra completely. Diastereotopic methylene protons with resolved (1)H NMR signals as well as protons of cyclohexane served as references for the construction of the spatial arrangement in the molecules. NOE contacts between protons attached to the stereocenter and the diastereotopic protons were thus used to determine the configuration of the molecules. Vicinal coupling constants (3)J assisted the assignment of the conformational arrangement of the cyclohexane ring of 4. 相似文献
15.
An array of NMR spectroscopy experiments have been carried out to obtain conformationally dependent (1)H,(13)C- and (13)C,(13)C-spin-spin coupling constants in the trisaccharide α-L-Rhap-(1 → 2)[α-L-Rhap-(1 → 3)]-α-L-Rhap-OMe. The trisaccharide was synthesized with (13)C site-specific labeling at C2' and C2″, i.e. in the rhamnosyl groups in order to alleviate (1)H spectral overlap. This facilitated the measurement of a key trans-glycosidic proton-proton cross-relaxation rate using 1D (1)H,(1)H-T-ROESY experiments as well as a (3)J(C, H) coupling employing 1D (1)H,(13)C-long-range experiments, devoid of potential interference from additional J coupling. By means of both the natural abundance compound and the (13)C-labeled sample 2D (1)H,(13)C-J-HMBC and (1)H,(13)C-HSQC-HECADE NMR experiments, total line-shape analysis of (1)H NMR spectra and 1D (13)C NMR experiments were employed to extract (3)J(C, H) , (2)J(C, H), (3)J(C, C), and (1)J(C, C) coupling constants. The (13)C site-specific labeling facilitates straightforward determination of (n)J(C, C) as the splitting of the (13)C natural abundance resonances. This study resulted in eight conformationally dependent coupling constants for the trisaccharide and illustrates the use of (13)C site-specific labeling as a valuable approach that extends the 1D and 2D NMR methods in current use to attain both hetero- and homonuclear spin-spin coupling constants that subsequently can be utilized for conformational analysis. 相似文献
16.
Marilu Dick‐Perez Tuo Wang Andre Salazar Olga A. Zabotina Mei Hong 《Magnetic resonance in chemistry : MRC》2012,50(8):539-550
Plant cell wall (CW) polysaccharides are responsible for the mechanical strength and growth of plant cells; however, the high‐resolution structure and dynamics of the CW polysaccharides are still poorly understood because of the insoluble nature of these molecules. Here, we use 2D and 3D magic‐angle‐spinning (MAS) solid‐state NMR (SSNMR) to investigate the structural role of pectins in the plant CW. Intact and partially depectinated primary CWs of Arabidopsis thaliana were uniformly labeled with 13C and their NMR spectra were compared. Recent 13C resonance assignment of the major polysaccharides in Arabidopsis thaliana CWs allowed us to determine the effects of depectination on the intermolecular packing and dynamics of the remaining wall polysaccharides. 2D and 3D correlation spectra show the suppression of pectin signals, confirming partial pectin removal by chelating agents and sodium carbonate. Importantly, higher cross peaks are observed in 2D and 3D 13C spectra of the depectinated CW, suggesting higher rigidity and denser packing of the remaining wall polysaccharides compared with the intact CW. 13C spin–lattice relaxation times and 1H rotating‐frame spin–lattice relaxation times indicate that the polysaccharides are more rigid on both the nanosecond and microsecond timescales in the depectinated CW. Taken together, these results indicate that pectic polysaccharides are highly dynamic and endow the polysaccharide network of the primary CW with mobility and flexibility, which may be important for pectin functions. This study demonstrates the capability of multidimensional SSNMR to determine the intermolecular interactions and dynamic structures of complex plant materials under near‐native conditions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
17.
Nowicka K Bujacz A Paluch P Sobczuk A Jeziorna A Ciesielski W Bujacz GD Jurczak J Potrzebowski MJ 《Physical chemistry chemical physics : PCCP》2011,13(14):6423-6433
In this work we present solid state data for five host-guest complexes formed by N-(4,19-dioxo-2,8,15,21-tetraoxa-5,18-diazatricyclohexacosa-1(25),9(14),10,12,22(26),23-hexaen-26-yl)-benzamide (1) belonging to the group of benzodiazacoronands, achiral compounds for which chiral crystals were found (J. Kalisiak and J. Jurczak, Cryst. Growth Des., 2006, 6, 20). The X-ray structure was resolved for four of them. It was found that 1 crystallizes in P2(1)/c, P1 and P2(1)/n achiral space groups. Differentiation of molecular packing and the presence of guest molecules within the crystal lattice were analyzed with solid state NMR. An attempt was made to correlate changes in (13)C δ(ii) and (15)N δ(ii) chemical shift tensor values, obtained from analysis of spinning sidebands of 1D and 2D (2D PASS) NMR spectra, with changes in the strength of hydrogen bonding. Quantum mechanical DFT GIAO calculations of NMR shielding parameters carried out on structures with coordinates taken from XRD were employed for signals assignment and verification of structural constraints. 相似文献
18.
《Magnetic resonance in chemistry : MRC》2003,41(12):1026-1029
Solid‐state cross‐polarization magic angle spinning 13C, 77Se and 15N NMR spectra were recorded for 1,3‐imidazolidine‐2‐selenone, its N‐substituted derivatives and some related compounds. The spinning sideband manifold intensities were used to obtain principal values of 13C and 77Se chemical shift tensors. Large selenium chemical shift anisotropies were observed for these selenones. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
19.
The non-classical 1,2-diboretane-3-ylidene 1a was studied by 13C and 29Si NMR spectroscopy in order to obtain coupling constants 1J(13C,11B) and 1J(29Si,13C). The magnitudes of 1J(13C,11B) were deduced from linewidth measurements in low-temperature 13C and 11B NMR spectra. Calculation of the coupling constants for model compounds related to 1a, using DFT methods based on optimized geometries [B3LYP/6-311+G(d,p)], gave data in agreement with the experiments. Furthermore, the calculations predict for the first time a negative sign of 1J(13C,11B) which mirrors the bonding situation in 1 as described by theory. 相似文献
20.
The 1H and 13C NMR spectra of 3-azabicyclo[3.3.1]nonanes with various oxygenated substituents at C-6 were assigned using 1D (DEPT) and 2D (COSY, HSQC, HMBC, NOESY) experiments. Close examination of this NMR data details the effects of substitution and stereochemistry at C-6 in these compounds. 相似文献